A cDNA clone encoding a human melanoma cell protein, AAMP-1, has been isolated using a monoclonal antibody, 1AA3, which was selected from earlier screening studies involving inhibition of tumor cell motility. The mAB, 1AA3, reacts strongly with a 95 kD protein and moderately with a 44 kD protein on immunoblots of A2058 whole cell lysates. It is possible that the 44 kD protein is a subunit of the larger protein. AAMP-1, the cDNA clone that we have sequenced, predicts a novel protein that is 44 kD. It has a potential transmembrane domain and exhibits significant homology (ALIGN Scores greater than 3.0, S.D. Protein Identification Resource program) to numerous immunoglobulin superfamily members (Ig kappa, Ig lambda, CD28, CD4, CD7, CD2, poly Ig receptor, NCAM, T cell receptor alpha, MAG, vaccinia virus, HT7, and link protein). Its single 1.6 Kb mRNA transcript is increased in activated human T cells. It is expressed in many human cell types, including metastatic melanoma cells, metastatic breast carcinoma, macrophages, fibroblasts, heart, brain, placenta, lung, liver, skeletal muscle, kidney, and pancreas. Several AAMP-1 regions have been found to have strong local homology with HIV-1 proteins including a region important in CD4 binding. These regions are "immunoglobulin-like" and these regions in AAMP-1 have been selected for further study with antipeptide antibodies. Currently, the AAMP-1 gene is being subcloned into a suitable vector for recombinant protein production of its 44 kD predicted product. The 95 kD protein mentioned earlier has been partially purified. A gene, approximately 1907 bp related to the AAMP-1 gene, has been isolated for further study.